Silica-alumina catalyst copromoted with palladium and iron-group metal, and isomerization process catalyzed thereby



United States Patent SlLICA-ALUMINA CATALYST COPROMOTED WITH PALLADIUM AND IRON-GROUP METAL, AND ISOMERIZATION PROCESS 'CATALYZED THEREBY Elmer L. Miller, Cary, and Hillis O. Folkins, Crystal Lake, [1]., assignors to The Pure OiI'Company, Chicago, 111., a corporation of Ohio Filed Nov. 27, 1957, Ser. No-699,272

10 Claims. (Cl. 260-63365) This invention relates to the catalytic hydroisomerization of isomerizable hydrocarbonsihaving lto 7 carbon atoms per molecule. It is more specifically concerned with improving the octane rating of petroleum hydrocarbon feed stocks consisting predominantly of normal hexane and/ or normal pentane hydrocarbons.

According to this invention, it has been found that the hydroisomerization of hydrocarbon feed stocks consisting predominantly of isomerizable aliphatic and alicyclic hydrocarbons having 4 to 7 carbon atoms per molecule can be efliciently carried out by processing the feed stocks at a temperature within the range of about .600 to 800 F. in the absence of appreciable hydrocracking, a pressure within the range of 100 to 1000 p.s.i.g., and a hydrogen/ hydrocarbon mol ratio within the range of about 0.5 to 5 in the presence of a composite catalyst consisting essentially of a silica-alumina base having high surface area and copromoted with small amounts up to about 2% by weight, based on said catalyst composition, of composite promoter consisting of palladium, and a group VIII metal of the iron series, e.g., cobalt, nickel, and iron, wherein the amount of the latter constituent is less than the amount of the former constituent and preferably does not exceed 0.6 of the weight of the former constituent.

In integrated petroleum refining operations for the productionof high-octane-number gasolines, in order'to obtain maximum effectiveness one of the unit processes selected must be for the processing of feed stocks consisting predominantly of the lower-molecular weight, normally liquid, aliphatic and alicyclic hydrocarbons containing 4 to 7 carbon atoms per molecule. Substantial quantities of these feed stocks are available to :warrant'ithe separate processing of these materials. Although octane number improvement can be obtained by treating-these feed stocks in a dehydrogenation process to produce olefins, it is more desirable from an octane-yield relationship to utilize isomerization processes for effecting the octane number improvement in these compositions. Furthermore, the isomerization product has an increasedmotor octane number and improved road performance, and is a stable product which augments the stability of the blended, finished gasoline.

Because of the importance of isomerization as a unit process in an integrated refining scheme for the production of high-octane-number gasolines, a number of commercial isomerization processes have been developed which utilize solid catalysts. The use of suchicatalysts eliminates plant corrosion problems and the accompanying high maintenance cost which are attendant upon the use of catalysts of the Friedel-Crafts type. The effectiveness of platinum-promoted, catalyst compositessuch as platinum-halogen-alurnina, platinum-silica-alumina, etc., in hydroforming operations, wherein isomerization is included as one of the concomitant reactions has prompted the utilization of these same catalysts in isomerization processes. These catalysts, however, require high operating temperatures which are disadvantageous because iso- Patented Ja n. 3, 1951 merization is an equilibrium reaction, the efficiency of which decreases with an increase in the processing temperature. As a result, at the high temperatures employed, the equilibrium product contains substantial quantities of low-octane-nurnber paraflins which were not isomerized during the course of the reaction. In addition, it has been reported that as the equilibrium conversion is approached, the gas loss increases very sharply. Further disadvantages resulting from the use of high-temperature processingconditions are higher fuel cost for carrying out the reaction, and added expense for fabricating process vessels to withstand the combination of high pressures and high temperatures required for this type of isomerization. A 'non-platinum-containing noble metal catalyst, however, has been found Which permits the isomerization reaction to be carried out at lower operating temperatures and thus avoids the disadvantages accompanying high-temperature isomerization using platinum catalysts.

It is therefore the primary objective of this invention to provide a hydroisomerization process for the isomerization of hydrocarbon feed stocks consisting predominantly of low-molecular-weight isomerizable hydrocarbons having 4 to 7 carbonatoms per molecule carried out at temperatures not in excess of about 800 F., in the substantial absence of hydrocracking. It is another of this invention to provide a relatively low temperature process for improving the octane number of petroleum-derived, feedstocks consisting essentially of C -C normal paraffinic hydrocarbons. It is an additional object of this invention to process low boiling, normally liquid, petroleum fractions in a hydroisomerization process employing a solid, non-corrosive catalyst utilizing relatively low tern peratures which permit the substantial production of branched-chain isomerization products with a minimum loss to gaseous products consisting of butanes and lowermolecular-weight hydrocarbons.

These and other objects will become more apparent from the following detailed description of this invention.

Figures land 2 are illustrative processing schemes employing theprocessof this invention.

As catalysts for use in isomerization processes employed in the upgrading of mixtures of saturated aliphatic and/ or alicyclic light hydrocarbons such as straight run, petroleum naphtha distillates to provide high-octane-number gasoline blending agents, it has been found that composites of hydrocarbon cracking catalysts and various hydrogenation catalysts are highly active andselectivc (see isomerization of Saturated Hydrocarbons in the Presence of Hydrogenation-Cracking Catalysts, Ciapetta et al., In-

dustrial and Engineering Chemistry, 45 (1) 147, et seq.). .Specific catalysts are prepared by incorporating a small amount of an hydrogenation agent in a refractory, mixed oxides base, composited to evince acidic properties, and hydrocarbon cracking activity. Although a .variety of suitable hydrogenation agents have been employed, the use of metallic nickel as the hydrogenation agent in the preparation of illustrative isomerization catalysts has pro, vided compositions which have high activity but poor selectivity unless specially prepared.

In a copending application of Folkins, Miller, and Lucas, Serial No. 691,996, filed October 23, 1957, entitled Process, there is described and claimed a hydroisomerization process which is carried out in the presence of a palladium-promoted silica-alumina catalyst which exhibits high activity and selectivity for the hydroisomeriization of suitable, isomerizable hydrocarbon containing feed stocks.

According to this invention, it has been found that the effectiveness of a palladiumpromoted, silica-alumina, composite isomerization catalyst can be enhanced by incorporating small amounts of a group VIII metal of the nickel or cobalt, is equal to or less than that of the major metal, i.e., does not exceed the amount of palladium in the catalyst. Maximum concentration of group VIII metal of the iron series should not exceed 0.6 percent of the weight of the catalyst. In most cases 0.4 percent or less, preferably in the range of 0.05 to 0.2 percent will be sufiicient. Under these limitations of concentration, the nickel, cobalt or iron acts as an activity promoter, but unexpectedly, no loss in selectivity obtains. Neither does the catalyst exhibit a tendency toward hydrocracking and thus require special activation and pretreatment procedures that are needed to modify this inherent characteristic of nickel catalysts.

In the preparation of catalyst compositions employed in the process of this invention, a variety of techniques have been devised and are described in the prior art. The palladium metal component in the co-promoter is incorporated in the acidic oxide support by impregnation of the support with a solution of a reducible palladium salt; such as the chloride or nitrate, or with a solution of a mixed palladium salt such as ammonium chloropalladite. The preparation of the supported catalyst is generally carried out by wetting the support with an aqueous solution of palladium chloride or in the alternative, an aqueous solution with dilute inorganic acid such as hydrochloric acid. The normality of the dilute acid should be in the range of about 0.1-4 normal and preferably within the range of 0.5-2 normal. The incorporation of the co-promoters can be effected either simultaneously or sequentially. In the latter instance either the group VIII metal or the metallic palladium can be initially introduced into the refractory, acidic, oxide support. To incorporate the metallic group VIII metal of the iron series, e.g., iron, nickel, or cobalt, in the selected refractory, mixed oxides base, the support is impregnated with a solution of a soluble group VIII metal salt such as the sulfate, acetate, chloride, nitrate of iron, nickel, or cobalt, or complex group VIII metal ammonium compounds. Another well known technique involves the use of the molten salt for impregnating the acidic, oxide carrier. The metallic group VIII metal is then produced by reducing the salts with a reducing gas such as hydrogen, carbon monoxide, hydrocarbons, etc. Another technique involves the admixing of a solution of a group VIII metal salt with the acidic, oxide carrier. A group VIII metal hydroxide or carbonate is then precipitated to efiect the impregnation of the acidic, oxide carrier. The resultant admixture is then filtered and the impregnated, acidic, oxide support washed free of soluble salts and dried, after which the metallic group VIII metal is produced by the reduction of the hydroxide or carbonate. In certain instances it may be preferred to initially convert the impregnated group VIII metal compound to the oxide by heating it in a suitable oxidizing atmosphere prior to reduction to the metallic state. An illustrative technique employing the oxidizing step involves impregnating an acidic, oxide base with a complex group VIII metal, ammonium salt solution, and thereafter contacting the impregnated, acidic, oxide carrier with carbon dioxide to produce the carbonate. The impregnated carrier is then dried and calcined at a temperature at which the carbonate will decompose to form the oxide, after which the oxide is subjected to reduction to form the metallic catalysts.

It is essential in preparing catalysts of this nature, wherein an ammonium compound is employed in the catalyst preparation, to utilize reducing conditions of time and temperature sufficient to effect the substantially complete removal of ammonium ions from the catalysts in order to avoid adversely affecting catalyst activity.

Prior to impregnating the activated, acidic, oxide support, it is preferred that this component of the catalyst composition be dried at an elevated temperature within the range of about 250-400 F. The activity of the catalyst can be further enhanced by calcining the silicaalumina support at a temperature of 800-1400 E, and preferably 8001200 F., to set the structure and remove the gel water. The support is then impregnated, and driedfor at least about 4 hours at a temperature within the range of about 225350 F. The green catalyst is then pelleted and activated by contacting the dried catalyst mass with a reducing gaseous stream such as hydrogen at an elevated temperature for a time sufficient to elfect the reduction of the palladium salt and the group VIII metal salt to the metallic state. This reduction can generally be carried out by heating the catalyst mass to a temperature between 750-975 F. in the presence of hydrogen for a period of at least about 2 hours. In this reducing step about 2000-5000 s.c.f.h. of hydrogen per barrel of catalyst is used.

The activated, silica-alumina base can be any suitable silica-alumina composition containing not less than about 50% by weight of silica which when composited evinces acidic properties and hydrocarbon cracking activity. It is preferred, however, to employ high-surface-area, e.g., not less than about square meters per gram, hydrocarbon cracking catalysts which have a silica content within the range of about 50-95% by weight, preferably 75-90% by weight, and an alumina content within the range of about 50-5%, and preferably 25-10%. The silica-alumina support can be obtained commercially or can be prepared by admixing separately prepared portions of silica-gel and alumina-gel or in the alternative by conventional coprecipitation techniques. (See Industrial and Engineering Chemistry, 44, 2860 (1952) and others). It is also possible that the catalyst which can be employed in the instant invention can be prepared by contacting silica-hydrogel particles with a solution of an aluminum salt and a palladium salt, and a salt of a group VIII metal in the desired concentration. After drying the mixture, it is heated for a sufficient time to effect the decomposition of the salts. Thereafter, the palladium and group VIII metal salts are reduced to the metallic state by treatment with hydrogen at elevated temperatures.

The process of this invention is especially adaptable for effecting the isomerization of feed stocks consisting predominantly of normal pentane and/or normal hexane to produce an octane improvement by promoting the molecular rearrangement of these hydrocarbons, or mixtures containing these hydrocarbons, such as light petroleum fractions having an ASTM boiling range of 100 F.-200 F.

To illustrate the instant invention a catalyst consisting essentially of 0.4% palladium and 0.4% nickel, incorporated on a silica-alumina cracking catalyst Was prepared as follows: Five grams of Ni(NO .6H O and 1.7 g. of PdCl were dissolved in 250 millimeters of distilled water containing 30 ml. of concentrated hydrochloric acid. A silica-alumina hydrocarbon cracking catalyst having the following characteristics was used as support.

5 "duced for use in a fluidizedsy'stem. To theasohition er nickel nitrate and palladium chloride were :addedZ-SO grams of support with vigorous mixing, thereby producing a slurry. The volume of impregnating solution employed represents the average amount necessary to .fill the-pore volume of the silica-alumina-support used. The impregnated support was dried at about-400 F. for 1;6"hours. The dried mass was pelleted into fis-inchiby"Ma-inch pellets and activated by heating to 975 F. inflhydrogen for a period of 5 hours followed by continued treatment with hydrogen at 975 F. for 16 hours, in order to insure a complete removal of the undesirableanions from the catalyst composition which might deleteriously-zafliect its activity. The reduced active catalyst waspurged-with nitrogen and cooled to 750 .F. Thereafter the catalyst was oxidized with air for 1 hour and allowed to cool to room temperature to facilitate handling. The catalyst was then placed in a reactor and heated:to.975'F. in hydrogen. Thereafter the catalyst :-was treated with l to 4 s.c.'f.h. of hydrogen .at;975 .F.rfor.;8 to .1 6 'hoursafter which it was cooled to 700 F. .Following'this, the reactor was pressurized to reaction temperature withrhydrogen, and the hydrocarbon feed stock.was charged under the desired condition. The effectiveness :of :the above catalyst composition as an isomerization catalyst was compared with other nickel catalysts and palladium catalysts prepared according to conventional catalyst preparation techniques. The results of this investigation are shown in Table 'I, in which is set. forth' comparative data demonstrating the superiority :of the co-promoted 'catalysts of our invention, .consisting'of metallic palladium and a group VII'I metal supported on silica-alumina, over other catalysts containing only one of these co-ipromoters.

Table I Catalyst Composition Promoter, Wt. Percent I 0.4Pd 0.4 Ni 0.4'Pd-- A Ni Support, Wt. Percent 75 SiO -25 A110 Run Conditions:

Temp, F Pressure, p.s.i.g LVHSV Hz/HO mol' ratio Feed, Wt. Percent:

i-C CQTI 'QISlOH Selectivity Catalyst Composition Promoter, Wt. Percent 1 0.4 Pd 0.4 Ni

Support, Wt. Percent 91 Run Conditions:

I'IQHG Idol ratio Feed, Wt. Percent:

1- 11-05 Cvclopentane. 1. 5" Conversio Yield. Selectivi To "further illustrate the instant invention, another -'-series of catalysts was prepared containing'OA-percent palladium and varying amounts of nickel on a high-:surface-area (450 m. gm.) silica-alumina support containing 13 percent alumina. These catalysts were tested in the isomerization of n-pentane at '500p.s.i.g. 3.0:LVHSV and at a H /hydrocarbon mol. ratio of 1.0. Thefollo ing results were obtained:

Percent Yield Percent 'Seleo- Percent Percent at-- tivity at- Pd Ni Support 700 F. 740 1?. 700 F. 740- F.

0.4 0 87/13 Sim/A120 43. 5 54. 8 98. 5 97. 1 0. 4 0. 1 87/13 Si02/Al20 52. l 57. 4 99. 6 98.1 0.4 0.2 87/13 SiOr/AlzO; 50.9 57.9 99.5 97.2 0. 4 0. 4 87/13 SiOz/AlzO; 45. 6 56-0 99. 3 '97, 5

Temperature, F. Range Preferred Range DOA 700-800 725-800 n-C 680-775 700-760 n-Cn 650-740 675-725 n-O- 670-725 625-700 Pressure, p.s.i.g 100-1, 000 350-750 Liq id hourly vol. space 0. 5-10 1-4 H /hydroearbon, mol ratio ,0. 5-5 1. 5-4. 5

1 The liquid volume of limiting reactant fed per hour per unit volume of effective catalyst bed.

It is evident that it mixed feed stocks are employed, a compromise must be effected in selecting the temperature which is to be used in order to produce optimum activity and selectivity without producing substantial amounts of hydrocracking as a concomitant, undesirable side reaction in the hydroisomerization process. A number of feed stocks have been investigated in order to define optimum operating conditions. These conditions for several'feeds are tabulated in Table II.

Table II Tempera- Total H /HG, Feed Description ture, F. Pressure, M01 LVHSV p.s.i.g. Ratio n-hexane, 20% cyclohexaue 725 645 3.2 2. 8 60% n-pentane-, 30% nhexane-, 10% cyclohexane. 725 700 2 2 An admixture consisting of: 63% n-pentane-, 30% n-hexane-, 10% cyclohexane diluted with 5% n-heptane 725 700 2 2 In the isomerization process of this invention a variety of processing schemes are available. In Figure 1 is shown a simple scheme which utilizes a feed preparation and product recovery system employing a minimum number of process towers. A light, straight-run naphtha having an ASTM boiling range of about -l80 F.-is introduced into de-isohexanizer 10 via line 11. The residue consisting essentially of n-hexane and heavier hydrocarbons is sent through line 12 to reactor 13 for isomer- 2 of line 14 to depentanizer 15 where the isohexanes and heavier hydrocarbons are separated and removed from the system via line 16 to storage. The overhead from depentanizer 15 which consists essentially of normal and isopentane is sent to C -splitter 18 through line 19. Isopentane is recovered in the fractionator overhead and is sent to storage or transferred to gasoline blending facilities (not shown) through line 20, and the residue consisting predominantly of normal pentane is transferred by means of line 21 to a point of confluence with line 12, wherein it is sent to reactor 13 for processing. effluent is initially treated in stabilizer 22 to separate the butane-and-lighter products. The butane-and-heavier fraction is then processed in de-isohexanizer 10 as described above.

It is also apparent that numerous combinations of reactors and fractionators are possible for carrying out the isomerization process of this invention for the processing of light hydrocarbon feed stocks. For example, an alternative processing scheme is shown in Figure 2. The process of this invention finds application in combination with other conventional, unit-refining processes, such as reforming, or with split-stream techniques employing a plurality of reactors to separately process feed stocks under isomerization conditions selected to obtain maximum efficiency with respect to the feed stock being processed. The various feed components can be processed jointly or singly, and on a once-through or recycle basis. In applications of this nature, the debutanized light, straight-run gasoline is deheptanized, either in existing equipment, such as a catalytic reformer feed preparation unit, or in new equipment. The C -C fraction is then split, and the C s, including debutanized C reactor eflluent, are split to produce an isopentane product and a normal pentane reactor feed. The degree of fractionation determines the product octane number, since normal pentane is recycled to extinction.

In the alternative, the C fraction can be employed in gasoline blending, or can be isomerized by one of two methods. Hexane fractions high in normal hexane content can be improved considerably by direct single-pass isomerization. Further improvement in octane number is possible by first splitting the isofrom the normal hexane, and then isomerizing the normal hexane fraction. Further octane improvement is possible by recycling normal hexane to extinction. This, however, would require an extra fractionation step to prevent an excessive build-up of methyl cyclopentane in the recycle stream.

An alternate method for processing normal pentane and the total hexane fraction in a single reactor involves deheptanizing a debutanized feed stock. The deheptan ized feed is deisopentanized, and the resultant stream passed through the reaction system. The debutanized reactor effiuent then is fractionated to produce an isomerized hexane fraction, and a pentane recycle stream which passes to the deisopentanizer. In this alternate processing, reaction conditions are determined by the more reac tive hexanes, resulting in a lower conversion per pass of normal pentane. The greater fractionation cost must be balanced by the decreased reactor section costs, since only one reaction section is required.

The relative quantities of pentanes and hexanes, as well as the iso-to-normal-hexane ratio determine which processing method is most economical.

To obtain maximum efliciency, auxiliary equipment is employed for pretreating the feed stock and the hydrogen utilized in the isomerization process. In order to insure long catalyst life, it is necessary to employ a hydrocarbon feed stock which is substantially free from sulfur or sulfur-containing compounds. Accordingly, a pretreater or guard case should be installed in the feed line to effect the removal of the sulfur compounds from the feed. Preferably, the pretreatment should be effected by a catalytic, vapor phase, desulfurization process in the presence of clay, bauxite, cobalt molybdate. or other suitable cata- The reaction 'in the presence of hydrogen.

lysts' for effecting the desulfurization of the feed stock A variety of desulfurization methods based upon the decomposition of the sulfur compounds at elevated temperatures in the vapor phase is briefly described by Kalichevsky, Petroleum Refiner, vol. 30 (4), at page 117, et seq. It is also preferred that the hydrogen employed as a processing aid in the hydroisomerization process be substantially free of water, 0 CO, H 8, and related compounds, including those which react under hydroisomerization conditions to form the above. Although it is preferred that the hydrogen be free of these impurities, trace amounts of these substances not in excess of about 2 parts per million can be tolerated. Although the foregoing invention is illustrated by a number of illustrative embodiments it is apparent to those skilled in the art that these are non-limiting examples and that other modificatoins can be made Without departing from the invention defined in the appended claims.

What is claimed is:

1. An isomerization catalyst consisting essentially of a silica-alumina catalyst, composited to evince acidic properties and hydrocarbon cracking activity, and copromoted with 0.011.0% by weight, based on total catalyst composition, of metallic palladium and a small amount of a group VIII metal of the iron series, wherein the amount by weight of the latter constituent is not greater than about 0.6 of the weight of the former constituent.

2. An isomerization catalyst consisting essentially of a silica-alumina catalyst, composited to evince acidic properties and hydrocarbon cracking activity and having a silica content within the range of about 50-95% by weight, based on saidsilica-alumina catalyst, 505% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.01-1.0% by weight of metallic palladium, base on total isomerization catalyst composition, and a small amount of a group VIII metal of the iron series not in excess of about 0.6 by weight of the palladium.

3. An isomerization catalyst consisting essentially of a silica-alumina catalyst, composited to evince acidic properties and hydrocarbon cracking activity, containing about by weight of silica, based on said silicaalumina catalyst, and 25% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.4% by weight of metallic palladium, based on isomerization catalyst composition, and 0.l-0.25% by weight of a group VIII metal of the iron series, based on total isomerization catalyst composition.

4. A composition in accordance with claim 3 in which the group VIII metal of the iron series is nickel.

5. A hydroisomerization process which comprises contacting a saturated hydrocarbon having 4-7 carbon atoms per molecule at a temperature within the range of about 600 to 800 F., a pressure Within the range of to 1000 p.s.i.g., and a hydrocarbon mol ratio within the range of 0.5 to 10 in the presence of an isomerization catalyst consisting essentially of a silica-alumina catalyst composited to evince acidic properties and hydrocarbon cracking activity and co-promoted with 0.01-1.0% by weight, based on total catalyst composition of metallic palladium, and a small amount of a group VIII metal of the iron series, wherein the amount by weight of the latter constituent is not greater than about 0.6 of the weight of the former constituent.

6. An isomerization process which comprises contacting an isomerizable saturated hydrocarbon having 4-7 carbon atoms per molecule at a temperature within the range of about 625 to 800 F., a pressure within the range of 350 to 750 p.s.i.g., and a hydrocarbon mol ratio within the range of 1.5 to 4.5 in the presence of an isomerization catalyst consisting essentially of a silica-alumina catalyst composited to evince acidic properties and hydrocarbon cracking activity and having a silica content within the ran e of about 50-95% by weight, based on said silica-alumina catalyst, 50-5% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.01-1.0% by Weight of metallic palladium, based on isomerization catalyst composition, and a small amount of a group VIII metal of the iron series not in excess of about 0.6 by weight of said metallic palladium.

7. An isomerization process which comprises contacting an isomerizable saturated hydrocarbon having 47 carbon atoms per molecule at a temperature within the range of about 625 to 800 F., a pressure Within the range of 350 to 750 p.s.i.g. in the presence of an isomerization catalyst consisting essentially of a silica-alumina catalyst composited to evince acidic properties and hydrocarbon cracking activity containing about 75% by weight of silica, based on said silica-alumina catalyst, and 25% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.4% by weight of metallic palladium, based on isomerization catalyst composition, and 0.1-0.25% by weight of a group VIII metal of the iron series, based on isomerization catalyst composition.

8. An isomerization catalyst consisting essentially of a silica-alumina catalyst, composited to evince acidic properties and hydrocarbon crackingactivity, containing about 87% by Weight of silica, based on said silica-alumina catalyst, and 13% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.4% by weight of metallic palladium, based on isomerization catalyst composition, and 0.10.2% by weight of a group VIII metal of the iron series, based on total isomerization catalyst composition.

9. An isomerization process which comprises contacting an isomerizable saturated hydrocarbon having 4-7 carbon atoms per molecule at a temperature within the range of about 625 to 800 F., a pressure within the range of 350 to 750 p.s.i.g. in the presence of an isomerization catalyst consisting essentially of a silica-alumina catalyst composited to evince acidic properties and hydrocarbon cracking activity containing about 87% by weight of silica, based on said silica-alumina catalyst, and 13% by weight of alumina, based on said silica-alumina catalyst, and co-promoted with 0.4% by weight of metallic palladium, based on isomerization catalyst composition, and 0.1-0.2% by weight of a group VIII metal of the iron series, based on isomerization catalyst composition.

10. A catalyst in accordance with claim 1 in which the group VHI metal is nickel.

References Cited in the file of this patent UNITED STATES PATENTS 2,005,412 Conolly et a1. June 18, 1935 2,550,531 Ciapetta Apr. 24, 1951 2,766,302 Elkins Oct. 9, 1956 2,834,823 Patton et a1. May 13, 1958 FOREIGN PATENTS 487,392 Canada Oct. 21, 1952 

1. AN ISOMERIZATION CATALYST CONSISTING ESSENTIALLY OF A SILICA-ALUMINA CATALYST, COMPOSITED TO EVINCE ACIDIC PROPERTIES AND HYDROCARBON CRACKING ACTIVITY, AND COPROMOTED WITH 0.01-1.0% BY WEIGHT, BASED ON TOTAL CATALYST COMPOSITION, OF METALLIC PALLADIUM AND A SMALL AMOUNT OF A GROUP VIII METAL OF THE IRON SERIES, WHEREIN THE AMOUNT BY WEIGHT OF THE LATTER CONSTITUENT IS NOT GREATER THAN ABOUT 0.6 OF THE WEIGHT OF THE FORMER CONSTITUENT. 